A Passive Optical Network (PON), as an optical access system, usually comprises an OLT located in a central office, a plurality of Optical Network Units (ONUs) located at a user side and an optical distribution network located between the OLT and the ONUs. The ONUs may operate in a time division multiplexing mode. For example, the OLT may control each one of the ONUs to send an uplink burst signal at different time slots. As external disturbance may also exist in an optical fiber line, in order to accurately receive an uplink burst signal sent by an ONU, the OLT may sample optical power of the uplink burst signal from the ONU based on an Received Signal Strength Indicator (RSSI) and may also determine the received optical power value. For example, if the received optical power value is in a proper threshold range, it may determine that the received signal is an uplink burst signal. Because of different distances between the ONUs and the OLT, the OLT may further adjust a receiving threshold of uplink burst signal according to the received optical power value.
An OLT may comprise an OLT system device and an OLT optical module. After an ONU is successfully registered in the OLT, the OLT system device may control the ONU to send an uplink burst signal in an assigned time slot, and a Media Access Control (MAC) chip of the OLT system device may send a MAC_Trigger signal to the OLT optical module in the corresponding time slot. Accordingly, the OLT optical module may sample optical power of a received uplink burst signal according to the MAC_Trigger signal. However, if attenuation of an optical link between the ONU and the OLT is too high or too low, the ONU may be failed to be registered in the OLT. When the ONU is failed to be registered, the OLT system device may not send the MAC_Trigger signal to the OLT optical module, so that the OLT optical module may be unable to sample the optical power of the uplink burst signal from the ONU.